Power magnetic devices, such as inductors and transformers, are employed in many different types of electrical circuits, such as power supply circuits for example. In practice, most power magnetic devices are fabricated of one or more windings, formed by an electrical member, such as a wire of a circular or rectangular cross section, or a planar conductor, which is wound or mounted to a bobbin of insulative material, e.g., plastic or the like. In some instances, the electrical member is soldered to terminations on the bobbin. Alternatively, the electrical member may be threaded through the bobbin for connection directly to a metallized area on a circuit board. A ferromagnetic core is typically affixed about the bobbin to impart a greater reactance to the power magnetic device.
As with other types of electronic components, there is a trend in the design of power magnetic devices towards achieving increased density and higher power. To achieve higher power, the resistance of the power magnetic device must be reduced, typically, by increasing the cross-sectional area of the electrical member forming the device winding(s). To increase the density of the power magnetic device, the bobbin is usually made very thin in the region constituting the core of the device to optimize the electrical member resistance. Conversely, the remainder of the bobbin is usually made thick to facilitate attachment of the electrical member to the bobbin terminals and/or to facilitate attachment of terminals on the bobbin to a circuit board. As a result of the need to make such a bobbin thin in some regions and thick in others, the bobbin is often subject to stresses at transition points between such thick and thin regions.
Another problem associated with present-day power magnetic devices is the lack of planarity of the device terminations. Because of the need to optimize the winding thickness of the power magnetic device in order to provide the requisite number of turns while minimizing the winding resistance, the thickness of the electrical member forming each separate winding of the device is often varied. The variation in the winding thickness often results in a lack of planarity of the device terminations, which is especially critical when the device is to be mounted onto a surface of a substrate such as a printed circuit board.
Thus, there is need for a power magnetic device which substantially overcomes the deficiency of past devices.